Color diffusion transfer with development controlling polymeric salt

ABSTRACT

Color diffusion transfer processes are carried out in the presence of a salt whose anion is derived from an immobile polymeric acid and whose cation is derived from a reagent adapted to control the development of silver halide.

United States Patent Sahatjian [451 Sept. 3, 1974 [54] COLOR DIFFUSIONTRANSFER WITH 3,575,699 4/1971 Bloom et all 96/3 DEVELOPMENT CONTROLLING3,598,600 8/1971 Tuites et al. 96/109 3,754,910 8/1973 Taylor 96/3POLYMERIC SALT Ronald A. Sahatjian, Bedford, Mass.

Polaroid Corporation, Cambridge, Mass.

Filed: Jan. 5, 1973 Appl. No.: 321,289

Inventor:

Assignee:

US. Cl 9673, 96/29 D, 96/77, 96/95, 96/109, .96/119 R Int. Cl. G03c7/00, G03c 5/54, G03c 1/40, GO3C 1/06, G03c l/34 Field of Search 96/3,29 D, 77, 95, 109

'- References Cited UNITED STATES PATENTS 10/1969 Rogers 96/3 PrimaryExaminer-Ronald H. Smith, I Assistant Examiner-Richai'd L. Schilling'Attorney, Agent, or Firm-Mart C. Matthews [57] ABSTRACT Color diffusiontransfer processes are carried out in the presence of a salt whose'anionis derived from an immobile polymeric acid and whose cation is derivedfrom a reagent adapted to control the development of silver halide.

46 Claims, No Drawings COLOR DIFFUSION TRANSFER WITH DEVELOPMENTCONTROLLING POLYMERIC SALT BACKGROUND OF THE INVENTION Various diffusiontransfer systems for forming color images have heretofore been disclosedin the art and need not be described in detail in this application.Generally speaking, such systems rely for color image formation upon adifferential in mobility or solubility of a dye image-providing materialobtained as a function of development of exposed silver halide so as toprovide an imagewise distribution of such material which is morediffusible and which is therefore selectively transferred, at least inpart, by diffusion, to a superposed dyeable stratum to impart theretothe desired color transfer image. The differential in mobility orsolubility may, for example, be obtained by a chemical action such as aredox reaction or a coupling reaction.

In any of these systems, multicolor iamges are obtained by employing afilm unit containing at least two selectively sensitized silver halideemulsions each having associated therewith a dye image-providingmaterial exhibiting desired spectral absorption characteristics. Themost commonly employed elements of this type are the so-called tripackstructures employing a blue-, a greenand a red-sensitive silver halidelayer having associated therewith, respectively, a yellow, a magenta anda cyan dye image-providing material.

A particularly useful system for forming color images by diffusiontransfer is that described in U.S. Pat. No. 2,983,606, employing dyedevelopers (dyes which are also silver halide developing agents) as thedye imageproviding materials. In such systems, a photosensitive elementcomprising at least one silver halide layer having a dye developerassociated therewith (in the same or in an adjacent layer) is developedby applying an aqueous alkaline processing composition. Exposed anddevelopable silver halide is developed by the dye developer which inturn becomes oxidized to provide an oxidation product which isappreciably less diffusible than the unoxidized dye developer, therebyproviding an imagewise distribution of diffusible dye developer in termsof unexposed areas of the silver halide layer, which imagewisedistribution is then transferred, at least in part, by diffusion, to adyeable stratum to impart thereto a positive dye transfer image.Multicolor images may be obtained with a photosensitive element havingtwo or more selectively sensitized silver halide emulsions andassociated dye developers, a tripack structure of the type describedabove and in various patents including the aforementioned U.S. Pat. No.2,983,606 being especially suitable for accurate color recordation ofthe original subject matter.

A number of diffusion transfer photographic processes have been proposedwherein the resulting photograph comprises the developed silver halideemulsions retained with the dye-image carrying layer as part of apermanent laminate. The image-carrying layer is separated from thedeveloped silver halide emulsions in said laminate by a light-reflectinglayer, preferably a layer containing titanium dioxide. Illustrative ofpatents describing such products and processes are the aforementionedUS. Pat. No. 2,983,606 issued Mar. 9, 1961 to Howard G. Rogers, US. Pat.Nos. 3,415,644, 3,415,645 and 3,415,646 issued Dec. 10, 1968 to Edwin H.Land, US. Pat. Nos. 3,594,164 and 3,594,165 issued July 20, 1971 toHoward G. Rogers,

and US. Pat. No. 3,647,347 issued Mar. 7,, 1972 to Edwin H. Land.

In the course of the above-described diffusion transfer processes, it isfrequently desirable to have certain reagents present so as to modifythe photographic and other properties of the transfer image, Inparticular, for example, one may wish to include a reagent whichcontrols or modifies the development of developable silver halide toobtain advantageous photographic results. As examples of these reagents,mention may be made of the various development restrainers or arrestors,antifoggants, etc., known to the art. Such development controllingreagents, however, may be capable of having additional and undesiredeffects if they are available too early in the process cycle or at toohigh a concentration, since these reagents frequently form relativelyinsoluble products with silver halide and could interfere with thedesired development of the exposed silver halide. While some reagents ofthis type are most effective for their intended purpose if used inrelatively larger quantities at higher temperatures than at roomtemperature, efforts to incorporate such larger quantities initially inthe processing composition frequently result in a reduction in thesensitivity or speed of the photosensitive element or other undesirableconsequences.

Methods have been proposed in the art for employment with multi-layereddiffusion transfer film units employing a common processing compositionwherein the particular reagent is made available or released to thesilver halide only after a predetermined period of time has elapsed fromthe application of the processing composition. As disclosed in US. Pat.No. 3,265,498, a reagent may be employed in a chemical form or in aphysical location such that its availability to the developable silverhalide is limited or restricted, e. g., as a result of the distancethrough which it must diffuse to reach the developing silver halide, oras a consequence of a significantly lower diffusion rate than thedeveloping agents. Thus, for example, US. Pat. Nos. 3,265,498

and 3,575,699 and copending applications of Bloom et al., Ser. No.60,272, filed Aug. 3, 1970 and Rickter, Ser. No. 214,665 filed Jan. 3,1972 all teach the use of hydrolyzable reagents, i.e., reagentprecursors which are substantially non-diffusible or at leastsubstantially less diffusible in their unhydrolyzed form than in theirhydrolyzed form. The reagent is therefore made available after thepredetermined period by hydrolysis of the precursor by the aqueousprocessing composition. However, this reliance on hydrolysis for reagentrelease has certain disadvantages, especially in high humidityenvironments where unintentional hydrolysis and undesirable migrationmay occur or in extremes of temperature where the rate of hydrolysis maybe effected.

It has been proposed in the art, for example, in the copendingapplication of Dec. et al., Ser. No. 263,539, filed June 16, 1972, toincorporate an onium salt of a polymeric anion in the film unit,preferably in the photosensitive element, in order to make the oniumcompound available immediately, yet avoid deleterious interaction withother components in the system during storage. However, it should benoted that the purposes of the processes described in the last-mentionedapplication are quite different from the present invention in that nodelay in the release of the reagent is desired or suggested.

BRIEF SUMMARY OF THE INVENTION The present invention makes it possibleto control and preferably delay the availability of a reagent whichcontrols the development of silver halide during the above-describedcolor diffusion transfer processes. This result is achieved by carryingout the processes in the presence of a salt comprising an anion derivedfrom a polymeric acid which is not diffusible from its location in thefilm unit and a cation derived from the development-controlling reagent.Upon contact with the processing composition, the reagent cation isrendered free to participate in the process. In accordance with thisinvention, a delay in the availability of a reagent may be effected,which delay is particularly valuable in the use of reagents tending toadversely affect image characteristics if made available in too large aquantity or too early in the process.

In a preferred embodiment, the polymeric acid anion is contained in aneutralizing layer of the imagereceiving element whose function is tolower the environmental pH of the film unit after a predetermined periodof time, thereby taking advantage of the timing mechanisms alreadyavailable in the film unit to control the timing of pH reduction. Thesalts of the present invention are not prone to the deficiencies of thehydrolyzable development restrainers with respect to high humidity andstorage contamination in unitary film structures and have been found tobe effective at high processing temperatures, for example, above 75 F.and especially over 100 F.

DESCRIPTION OF THE PREFERRED EMBODIMENT As indicated above, the presentinvention is directed to carrying out the color diffusion transferprocesses previously described in the presence of a salt which comprisesan anion derived from an immobile polymeric acid and a cation derivedfrom a reagent adapted to control the development of silver halide.

It has been stated that the employment of such a development controllingreagent in.color diffusion transfer processes is particularly desirableif the reagent is made available in a controlled manner at apredetermined time. By means of the present invention, an advantageousand controlled release of the reagent may be accomplished, yet thisreagent is provided in such a chemical form that it can be convenientlydisposed in the film unit, particularly an integral positive-negativefilm unit, in a photographically inactive or unavailable state as aconsequence of its non-diffusible polymeric anion, thus insuring thedesired stability and sensitivity of the film unit upon prolongedstorage. The active development controlling function is effectivelyrendered unavailable in the salt form with respect to prematureinteraction with the silver halide, i.e., what is referred to ascontamination effects are avoided. However, the cation of the salt ismade readily available to diffuse in the processing composition to thesilver halide upon contact with the alkali of the processingcomposition.

Generally speaking, the salts of the present invention comprise thereaction product of an immobile polymeric acid and a developmentcontrolling reagent, both of which are described in greater detailhereinbelow.

These salts are believed to be formed as a result of the loss of theacid hydrogen of one or more of the pendant acid groups of the polymericacid to form a negatively charged radical, i.e., an anion, and thesubsequent replacement of that hydrogen by a positively charged radical,i.e., a cation, derived from the protonation of the developmentrestrainer.

Reagents which are suitable for forming cations within the scope of thisinvention are derived from a wide variety of known compounds whichcontrol the development of silver halide. In general, these reagentswill form products or complexes with undeveloped silver halide, whetherexposed or unexposed, which products are substantially less developableeither photolytically or by a silver halide developing agent, e.g., by adye developer, and which are substantially insoluble,

and hence essentially non-diffusible, i.e., diffusible only withdifficulty. Illustrative examples of such reagents are the so-calleddevelopment arrestors, antifoggants,

etc.

The selected reagent must also be capable of protonation at a pHprovided by the polymeric acid employed, i.e., a pH below 7, and mostpreferably in the range of about 2 to about 5, in order to form a saltwithin the context of this invention.

Particularly useful reagents described in the art as performingdevelopment controlling functions may be characterized as azolecompounds, i.e., compounds having a 5-membered ring containing at leastone atom of nitrogen. As examples of such azole compounds mention may bemade of the various imidazoles, triazoles and tetrazoles known to theart and, especially in diffusion transfer systems, the4-azabenzimidazoles such as disclosed in US. Pat. Nos. 3,473,924 and3,687,660. Numerous examples of such reagents are described in thediffusion transfer art and those skilled in this art may readily selectcompounds which may be usefully employed by following the teachings ofthis invention.

One group of preferred reagents for the practice of this invention isdisclosed in the copending application of Land et al, Ser. No. 246,669,filed Apr. 24, 1972 and its parent application Ser. No. 211,718, filedDec. 23, 1971, now US. Pat. No. 3,785,814. These reagents may begenerically described as 6-alkylamino purines of the formula:

LNJLN/ wherein R is an alkyl group, it being understood that alkyl isintended to include aralkyl, such as OCH:

Where the alkyl group is a simple alkyl group, better results aregenerally obtained when the alkyl group contains more than one or twocarbons. As will be apparent from the above, the alkyl group may besubstituted, e.g., by halogen, alkoxy, etc.

The above compounds have found advantageous employment with sulfur-freesilver solvents such as 6- methyl uracil to prevent undesired reactionsin integral film units, such as photolytic darkening of white areas, asdescribed in detail in the application Ser. No. 21 1,718 mentionedabove. In addition, the 6- alkylamino purines also have been found to beextremely effective in maintaining maximum dye density in dye developertransfer images, particularly when processing is conducted attemperatures above room temperature, i.e., at temperatures above 75 F.These reagents are soluble in alkaline media and have beenadvantageously disposed in the processing composition. They have beenfound to be useful without conventional antifoggants also being present,although such antifoggants may be useful in varying the sensitometry ofa given photographic system.

The compound providing the anion in the present invention may beselected from a variety of immobile or non-diffusible polymeric organicacids, that is, those acids having a polymeric backbone with pendantacid groups thereon such as carboxyl groups, sulfonic acid groups, andthe like. Most preferably, as will be described in more detailhereinafter, the salt comprising an anion of the polymeric acid and acation of a reagent described above is employed as an acid-reactingreagent in a layer of the film unit which is adapted to lower theenvironmental pH after a predetermined period of time. An extensivelisting of polymeric acids suitable for this pH reduction function andcontemplated as useful in the practice of this invention may be found,for example, in U.S. Pat. No. 3,362,819. The most useful acid polymersare characterized as providing free acid groups, for example, carboxylgroups, and as being substantially non-diffusible in an aqueous medium,yet having solubility in a solvent which is sufficiently polar to allowthe formation of a salt with one of the abovedescribed reagents. Thepolymeric acid selected should provide a pH sufficient to protonate thereagent, Le, a pH below 7 and most preferably a pH in the range fromabout 2 to about 5. As examples of specific polymeric acids contemplatedas suitable for use in this invention, mention may be made ofpolystyrene sulfonic acid, polyacrylic acid, and acid derivatives ofmethyl vinyl ether/maleic anhydride and poly (ethylene/maleicanhydride).

The present invention is applicable to a wide variety of color diffusiontransfer processes and the arrangement and order of the individuallayers of the film used in such color processes may vary in many ways asis known in the art. For convenience, however, the more specificdescription of the invention may be by use of the preferred dyedeveloper diffusion transfer color processes and of integralnegative-positive film units of the type contemplated in the previouslymentioned U.S. Pat. No. 3,415,644.

In such color diffusion transfer systems, color transfer images areobtained by exposing a photosensitive element, sometimes referred to asa negative component, comprising at least a light-sensitive layer, e.g.,a gelatino silver halide emulsion layer, having an image dye-providingmaterial associated therewith in the same or in an adjacent layer, toform a developable image; developing this exposed element with aprocessing composition to form an imagewise distribution of a diffusibleimage dye-providing material; and transferring this imagewisedistribution, at least in part, by diffusion, to a superposedimage-receiving element, sometimes referred to as a positive component,comprising at least a dyeable stratum to provide a color transfer image.The negative and positive components initially may be carried onseparate supports which are brought together during processing andthereafter retained together as the final integral negative-positivereflection print, or preferably they may initially comprise a unitarystructure, e.g., integral negative-positive film units wherein thenegative and positive components are part of a photosensitive laminateor they may otherwise be physically retained together in superposedrelationship prior to, during and after image formation. (Procedures forforming such film units wherein the positive and negative components aretemporarily laminated together prior to exposure are described, forexample in U.S. Pat. No. 3,652,281 to Albert J. Bachelder and FrederickJ. Binda and in U.S. Pat. No. 3,652,282 to Edwin H. Land, both issuedMar. 28, 1972). In the preferred embodiments, the positive component isnot removed from the negative component for viewing purposes, althoughthis invention is'contemplated as suitable for those diffusion transferprocesses where this occurs. The preferred film units comprise aplurality of layers including a negative component comprising at leastone light-sensitive silver halide and associated dye-developer as thedye image-providing material and a positive component comprising atleast a dyeable stratum. As indicated above, these components may belaminated together or otherwise secured together in physicaljuxtaposition as an essentially integral structure. Film units intendedto provide multicolor images comprise two or more selectively sensitizedsilver halide layers each having associated therewith an appropriatedye-developer providing an image dye spectral absorption characteristicssubstantially complementary to the light by which the associated silverhalide is exposed. The most commonly employed negative components forforming multicolor images are of the tripack structure and containblue-, greenand red-sensitive silver halide layers each havingassociated therewith in the same or in a contiguous layer a yellow, amagenta and a cyan dye-developer respectively. Interlayers or spacerlayers may, if desired, be provided between the respective silver halidelayers and associated dyedevelopers or between other layers.

In addition to the aforementioned layers, such film units furtherinclude means for providing a reflecting layer between the dyeablestratum and the negative component in order to mask effectively thesilver image or images formed as a function of development of the silverhalide layer or layers and also to mask image dyeproviding materialwhich is not transferred, thereby providing a background, preferablywhite, for viewing the color image formed in the dyeable stratum,without separation, by reflected light. This reflecting layer maycomprise a preformed layer of a reflecting agent included in the filmunit or the reflecting agent may be provided after photoexposure, e. g.,by including the reflecting agent in the processing composition. The dyetransfer image is then viewable through a dimensionally stableprotective layer or support. Most preferably another dimensionallystable layer or support, which may be transparent or opaque, ispositioned on the opposed surface so that the aforementioned layers arebetween a pair of dimensionally stable layers or support members, one ofwhich is transparent to permit viewing therethrough of the colortransfer image.

The liquid processing composition referred to for effecting multicolordiffusion transfer processes comprises at least an aqueous solution ofan alkaline material, for example, sodium hydroxide, potassiumhydroxide, and the like, and preferably possessing a pH in excess of 12,and most preferably includes a viscosityincreasing compound constitutinga film-forming material of the type which, when the composition isspread and dried, forms a relatively firm and relatively stable film.The preferred film-forming materials disclosed comprise high molecularweight polymers such as polymeric, water-soluble ethers which are inertto an alkaline solution such as, for example, a hydroxyethyl celluloseor sodium carboxymethyl cellulose. Other filmforming materials orthickening agents whose ability to increase viscosity is substantiallyunaffected if left in solution for a long period of time are alsocapable of utilization. As stated, the film-forming material ispreferably contained in the processing composition in such suitablequantities as to impart to the composition a viscosity in excess of 100cps. at a temperature of approximately 24 C. and preferably in the orderof 100,000 cps. to 200,000 cps. at that temperature.

A rupturable container of known description contains the requisiteprocessing composition and is adapted upon application of pressure torelease its contents for development of the exposed film unit, e.g., bydistributing the processing composition in a substantially uniform layerbetween a pair of predetermined layers. In film units providing anintegral negativepositive reflection print, a processing compositioncontainin g a white pigment may be distributed between the dyeablestratum and the negative component to provide the light-reflectinglayer.

A preferred opacification system to be contained in the processingcomposition to effect processing outside of a camera is that describedin the above-mentioned U.S. Pat. No. 3,647,437, and comprises adispersion of an inorganic light-reflecing pigment which also containsat least one light-absorbing agent, i.e., optical filter agent, at a pHabove the pKa of the optical filter agent in a concentration effectivewhen the processing composition is applied, to provide a layerexhibiting optical transmission density greater than about 6.0 densityunits with respect to incident radiation actinic to the photosensitivesilver halide and optical reflection density greater than about 1.0density units with respect to incident visible radiation.

In lieu of having the light-reflecting pigment in the processingcomposition, the light-reflecting pigment used to mask thephotosensitive strata and to provide the requisite background forviewing the color transfer image formed in the receiving layer may bepresent initially in whole or in part as a preformed layer in the filmunit. As an example of such a preformed layer, mention may be made ofthat disclosed in U.S. Pat. No. 3,165,421 issued Oct. 26, 1971 and inU.S. Pat. No. 3,620,724 issued Nov. 16, 1971, both in the name of EdwinH. Land. The reflecting agent may be generated in situ as is disclosedin U.S. Pat. Nos. 3,647,434 and 3,647,435, both issued Mar. 7, 1972 toEdwin H. Land.

The dye developers (or other image dye-providing substances) arepreferably selected for their ability to provide colors that are usefulin carrying out subtractive color photography, that is, the previouslymentioned cyan, magenta and yellow. They may be incorporated in therespective silver halide emulsion or, in the preferred embodiment, in aseparate layer behind the respective silver halide emulsion. Thus a dyedeveloper may, for example, be in a coating or layer behind therespective silver halide emulsion and such a layer of dye developer maybe applied by use of a coating solution containing the respective dyedeveloper distributed, in a concentration calculated to give the desiredcoverage of dye developer per unit area, in a filmforming natural, orsynthetic, polymer, for example, gelatin, polyvinyl alcohol, and thelike, adapted to be permeated by the processing composition.

Dye developers are compounds which contain the chromophoric system of adye and also a silver halide developing function. By a silver halidedeveloping function is meant a grouping adapted to develop exposedsilver halide. A preferred silver halide development function is ahydroquinonyl group. Other suitable developing functions includeortho-dihydroxyphenyl and ortho-and para-amino substituted hydroxyphenylgroups. In general, the development function includes a benzenoiddeveloping function, that is, an aromatic developing group which formsquinonoid or quinone substances when oxidized.

The dyeable stratum, or image-receiving layer, may comprise one of thematerials known in the art, such as polyvinyl alcohol, gelatin, etc. Itmay contain agents adapted to mordant or otherwise fix the transferredimage dye(s). Preferred materials comprise polyvinyl alcohol or gelatincontaining a dye mordant such as poly-4-vinylpyridine, as disclosed inU.S. Pat. No. 3,148,061, issued Sept. 8, 1964 to Howard C. Haas. If thecolor of the transferred image dye (s) is affected by changes in pH, thepH of the image layer may be adjusted to provide a pH affording thedesired color.

The nature of the chemical form in which the development controllingreagent is provided in the present invention allows for greatflexibility in its utilization and placement in the film unit. Thisflexibility enables the operator to vary substantially the timing of therelease of development controlling reagent, and the quantity madeavailable to the silver halide, in accordance with, for example, thesensitometry desired or the processing temperatures to be encountered.

In the various color diffusion transfer systems which have previouslybeen described and which employ an aqueous alkaline processing fluid, itis well known to employ an acid-reacting reagent in a layer of the filmunit to lower the environmental pH following substantial dye transfer inorder to increase the image stability and/or to adjust the pH from thefirst pH at which the image dyes are diffusible to a second (lower) pHat which they are not. For example, the previously mentioned U.S. Pat.No. 3,415,644 discloses systems wherein the desired pH reduction may beeffected by providing a polymeric acid layer adjacent the dyeablestratum. These polymeric acids may be polymers which contain acidgroups, e.g., carboxylic acid and sulfonic acid groups, which arecapable of forming salts with alkali metals, such as sodium, potassium,etc., or with organic bases, or potentially acid-yielding groups, suchas anhydrides or lactones, or other groups which are capable of reactingwith bases to capture and retain them. The acid-reacting group is, ofcourse, non-diffusible from the acid polymer layer.

As previously indicated, the salt of the present invention is preferablydisposed in this neutralizing layer, and most preferably theabove-mentioned polymeric acid of the neutralizing layer serves toprovide the anion of the salt. Preferably, all of the free acid groupsof the selected polymeric acid are not converted to the salt form inthis embodiment of the invention. However, essentially all of the acidgroups may be so converted, if desired, since the acid groupsneutralized by salt formation are still available to capture alkali ionfrom the processing composition by cation exchange to accomplish the pHreduction function of the neutralizing layer. The acid salts arepreferably formed by reacting somewhat less than a stoichiometricquantity of the selected reagent with the polymeric acid of theneutralizing layer. For convenience, this reaction may be carried out inthe medium which serves as the coating solution for the neutralizinglayer prior to its coating. As previously noted, it is contemplated thatthe salt of this invention may be disposed in a variety of locations inthe film unit, in which case the salt may be formed apart from a coatingsolution and subsequently'distributed in the coating solution of anyappropriate layer.

It will be appreciated that in the preferred embodiment described abovethe amount or degree to which the active hydrogens of the polymeric acidare replaced with the reagent cation will be at least in part dependentupon the amount of reagent needed in the particular film unit and systemin which these salts are employed. The lesser the amount of thisreplacement the fewer the reagent cations which will be present for agiven coverage of the acid salt. It will be readily apparent that theappropriate amount of reagent needed may be determined by routineexperimentation.

The pH of the processing composition may be of the order of at least 12to 14, and it preferably contains a larger concentration of sodiumand/or potassium ions. The neutralizing layer should therefore containat least sufficient acid groups to effect a reduction in the pH of theimage layer from a pH of about 12 to 14 to a pH of at least 1 l or lowerat the end of the imbibition period, and preferably to a pH of about to8 within a short time after imbibition, thus requiring, of course, thatthe acidic action of the salt of this invention be accurately socontrolled as not to interfere with either development of the negativeor image transfer of the color-providing material. For this reason, thepH of the image layer should be kept ata functional transfer level untildye image has been formed. Where the colorproviding material is notdiffusible at the lower pH obtained by the polymeric acid layer, thesubsequent pH reduction, in addition to its desirable effect upon imagelight stability, also serves a highly valuable photographic function bysubstantially terminating further dye transfer.

In order to prevent premature pH reduction during transfer processing,or premature release of the devel opment controlling reagent cation, theacid groups may be so distributed in the neutralizing layer that therate of their availability to the alkali is controllable, e.g., as afunction of the rate of swelling of the polymer layer which rate in turnhas a direct relationship to the diffusion rate of the alkali ions. Thedesired distribution of the acid groups in the acid polymer layer may beeffected by mixing the acid polymer with a polymer free of acid groups,or lower in concentration of acid groups, and compatible therewith, orby using an acid polymer having a relatively lower proportion of acidgroups.

The layer containing the polymeric acid may also contain awater-insoluble polymer, preferably a cellulose ester, which acts tocontrol or modulate the rate at which the alkali reacts with the acidgroups, free or neutralized by salt formation. As examples of celluloseesters contemplated for use, mention is made of cellulose acetate,cellulose acetate butyrate, etc. The particular polymers andcombinations of polymers employed in any given embodiment are, ofcourse, selected so as to have adequate wet and dry strength and whennecessary or desirable, suitable subcoats are employed to help thevarious polymeric layers adhere to each other during storage and use.

in addition, an inert interlayer or spacer layer also may be and ispreferably disposed between the neutralizing layer and the dyeablestratum in order to control or time the pH reduction so that it is notpremature and interfere with the development process. Suitable spacer ortiming layers for this purpose are described with particularity in U.S.Pat. Nos. 3,362,819; 3,415,644; 3,419,389; 3,421,893; 3,455,686; and3,575,701. v

This timing is disclosed as being a function of the rate at which alkalidiffuses through the inert spacer layer. It has been found that the pHdoes not drop until the alkali has passed through the spacer layer,i.e., the pH is not reduced to any significant extent by the merediffusion into the timing layer, but the pH drops quite rapidly once thealkali diffuses through this spacer layer. The timing layer preferablycomprises a permeable polymeric film-forming material whose permeabilitycharacteristics may be either directly or inversely dependent on changesin temperature as described in detail in the aforementioned U.S.Patents.

In the context of the present invention, the permeabilitycharacteristics exhibited by the timing layer as a function oftemperature is a matter of choice for one practicing the invention,depending in a large part on the intended function of the developmentcontrolling reagent being introduced. To illustrate, a reagent may bedesired to be made available in increasingly larger quantities as theprocessing temperature increases so as to reduce the fog associated withthe higher temperatures, and thus maintain transfer image density. Sucha high temperature antifoggant may require the selection of a timinglayer whose permeability increases in direct relation with theprocessing temperature so as to make more of the reagent available athigher temperatures. On the other hand, if the reagent introduced intothe process is for another purpose, for example, for arresting alldevelopment of silver halide after a predetermined period of time,increased permeability of the timing layer with temperature would mostlikely result in the premature introduction of the reagent therebyinterfering with the desired imagewise development of silver halide.With such a development arrestor, therefore, one may desire atemperature-inverting timing layer whose permeability decreases underconditions of increasing temperature.

The salts of this invention may be applied in accordance withconventional coating techniques. It is most preferable to employpolymeric salts which are watersoluble and which may therefore be formedin aqueous coating solutions, thereby obviating the need for organicsolvents and the obvious manufacturing disadvantages inherent in the useof organic coating solutions, e.g., the need for special equipment tohandle these solvents which are typically volatile, including thestorage thereof before use, and the involved danger in the use of suchsolvents. However, the coating disadvantages do not preclude the use ofwater-insoluble polymeric salts which need be coated from organicsolutions, and from a photographic standpoint, these water-insolublesalts may be equally applicable and are therefore contemplated by thepresent invention. It should be apparent that whether water-soluble orwater-insoluble salts are employed, the salt itself is not diffusiblefrom its location in the film unit, whereas the free reagent cation ischaracterized as being soluble and diffusible in the alkaline processingcomposition, at least while the pH is basic, e.g., above about pH 9.

As was heretofore mentioned, the neutralizing layer of this invention isuseful in systems wherein the photosensitive strata and the dyeablestratum are contained on separate elements; and in systems wherein theyare contained together as a unitary film unit, e.g., in the integralnegative-positive film units previously described. In the former type,the neutralizing layer is most preferably contained in association withthe dyeable stratum, e.g., in an image-receiving element comprising asupport carrying the neutralizing layer and the dyeable stratum with aspacer or timing layer preferably being disposed therebetween. It mayhowever be contained as a layer in the photosensitive element, i.e., inthe element containing the photosensitive strata, as is disclosed in US.Pat. No. 3,362,821. In like manner, in the integral negative-positivefilm units, the neutralizing layer is preferably associated with thedyeable straturn, e.g., on the side of the dyeable stratum opposed fromthe negative component, and most preferably a timing layer is disposedbetween the neutrailizing layer and dyeable stratum. I

A particularly useful embodiment of this invention employs a saltcomprising the reaction product of 6- benzylamino purine:

@w N fl A and the half butyl ester of the poly (ethylene/maleicanhydride) copolymer having the repeating units:

The salt is preferably disposed in a neutralizing layer which ispositioned on the side of the dyeable stratum of the preferred integralnegative-positive film units just described which is opposed to thephotosensitive strat. The 6-benzylamino purine salt has been found to beuniquely suited for such placement without exhibiting the contaminationeffects which result from the undesirable diffusion of a developmentcontrolling reagent from the image-receiving element to thephotosensitive element upon storage. The preferred salt is characterizedas being soluble in the aqueous acidic medium of the neutralizing layer,i.e., about pH 2, with all the attendant coating benefits describedabove, and also provides a soluble and diffusible cation upon contactwith the alkaline processing composition (pH about 13 to 14). The cationremains soluble and diffusible in the processing composition while theenvironmental pH is maintained at a level above about pH 9. However, the6-benzylamino purine is substantially insoluble and non-diffusible atneutral pH levels, i.e., around pH 7.

It is to be remembered that the polymeric acid anion is non-diffusiblefrom the neutralizing layer and therefore prevents migration of thesalt, as such, from the neturalizing layer. Thus, the'6-benzylaminopurine is immobilized and made unavailable until contacted by theprocessing composition. As described before, this reagent isparticularly useful in maintaining transfer image density, especially attemperatures above F., e.g. 100 F. or above. Since the entire quantityneeded to provide an acceptable density at such high temperatures, ifincluded solely in the processing composition, may cause a reduction inphotographic speed at room temperature, the present invention may beconveniently employed to meter out the required supplemental amount ofreagent at a controlled rate under conditions of increasing temperature.9

The present invention will be further illustrated by the followingexamples; however, it is understood that the scope of this invention isnot limited to the details therein set forth.

EXAMPLE 1 The polymeric saltof 6-benzylamino purine was prepared byadding to an aqueous acidic (about pH 2) coating solution comprising thehalf butyl ester of poly (ethylene/maleic anhydride), about mg. of 6-benzylamino purine per gram of said ester. The resultant solution wascoated at a coverage of about 2,500 mgs/ft. on a transparent 4 milpolyethylene terephthlate film base to provide the neutralizing layer ofan image-receiving element. Over this layer, were coated, in succession:

l. a timing layer containing about a 40:1 ratio of a 60-30-4-6 copolymerof butylacrylate, diacetone acrylamide, styrene and methacrylic acid,and polyacrylamide, at a coverage of about 500 mgs./ft. and

2. a polymeric image-receiving layer containing a 2:1 mixture, byweight, of polyvinyl alcohol and poly-4- vinylpyridine, at a coverage ofabout 300 mgs./ft.

The element so prepared was immersed in an aqueous alkaline solution ofpotassium hydroxide at a pH of about 9 for about 3 minutes at roomtemperature. The release of 6-benzylamino purine from the element intothe solution was confirmed by a UV. spectrum of the solution, whichindicated the presence of 6- benzylamino purine.

EXAMPLE 2 An additional image-receiving layer was prepared as describedin Example 1 without forming the salt of the 6-benzylamino purine in thecoating solution for the neutralizing layer, to serve as a control forthe test image-receiving element of Example 1.

An aqueous laminating solution was prepared comprising about 5 parts ofwater to 1 part (by weight) of polyethylene glycol having a molecularweight range of about 6,000 to 7,500 (commerically available from UnionCarbide Corp. under the tradcname Carbowax 6000) The test and controlimage-receiving elements were then each bonded to photosensitiveelements of identical structure to form a laminate by distributing theabove-prepared laminating solution between the top layers of saidelements at a coverage of about 25 mg./ft. as they were brought face-toface at the nip of pressure-applying rollers, all according to theteachings of the copending application of E. H. Land, Ser. No. 247,023,filed Apr. 24, 1972, now US. Pat. No. 3,793,023. The laminates thusformed were stored for 5 days at 100 F. and 90 percent relativehumidity, exposed to an analytical target andprocessed with an aqueousalkaline processing composition. The sensitometric results showedessentially no deleterious effects from the storage of the test elementwhen compared with the control, thereby indicating the absence of anundesired migration of the 6-benzylamino purine from the testimage-receiving element during storage.

EXAMPLE 3 The test and control image-receiving elements described inExample 2 were each taped together with a photosensitive element to forman integral film unit. Each photosensitive element comprised thefollowing, in sequence, on an opaque film base:

1. A layer comprising the cyan dye developer:

2. A red-sensitive gelatino silver iodobromide emulsion.

3. An interlayer of a 60-30-4-6 copolymer of butylacrylate, diacetoneacrylamide, styrene and metacrylic acid, and polyacrylamide.

4. A layer comprising the magenta dye developer:

5. A green-sensitive gelatino silver iodobromide emulsion layer.

6. A layer containing the copolymer referred to above in layer 3 andpolyacrylamide.

7. A layer comprising the yellow dye developer:

8. A blue-sensitive gelatino silver iodobromide emulsion layer; and

9. A layer of gelatin.

Each film unit was provided with a rupturable container retaining anaqueous alkaline processing solution and fixedly mounted on the leadingedge thereof so that, upon application of compressive pressure to thecontainer to rupture the containers marginal seal, its contents weredistributed in a layer approximately 0.0028 inch thick between theimage-receiving layer and the gelatin overcoat layer of thephotosensitive component. The aqueous alkaline processing compositioncomprised:

-0001. Hood-f 2. U

CIBIISTOK/ and, water to make 100 g.

Each film unit was exposed to an analytical target through thetransparent support and the layers thereon. The processing of the filmunits was accomplished by passing each film unit between a pair ofpressureapplying rollers into a lighted room at room temperature. Thelaminate obtained by distribution of the processing composition wasmaintained intact to provide an integral negative-positive reflectionprint.

The reflection densities to red, green and blue light were measuredabout 60 minutes after processing by an automatic recording densitometerwhich plotted the characteristic positive H+D curves relating thelogarithm of the original exposure of the negative to the reflectiondensities of the positives. The following table summarizes the resultsobtained for the maximum reflection density (D obtained with each color,the log exposure value determined at a density of 0.75 (0.75 speed) foreach color and the algebraic differences obtained when the green speedvalues as just defined were subtracted from the red speed values (redbalance) and from the blue speed values (blue balance):

Table 1 shows that when the sole source of the 6- benzylamino purine wasthe salt disposed in the test image-receiving element, about 0.15 to0.20 more D than the control without the salt was obtained at roomtemperature, with more acceptable sensitometric speed and balance.

16 EXAMPLE 4 Test and control film units were fabricated and exposed asdescribed in Example 3. The processing of the film units wasaccomplished by passing each film unit between the aforementioned pairof pressure-applying rollers into a lighted area at temperatures of 40 FF (room temperature), F. and into a 1 15 F. water bath. The film unitswere then sensitometrically evaluated as described in Example 3.

6-benzy1amino purine was included in the processing composition employedfor both test and control film units, in addition to including thepolymeric salt of 6- benzylamino purine in the neutralizing layer of thetest image-receiving element. The processing composition comprised:

ethyl-N,N-ethylcne glycine COOH HOOC-A 2.71g. CXSHWO g/ and water tomake 100 g.

. The following table summarizes the sensitometric results:

It can be seen from the data in Table 2 that additional 6-benzylaminopurine located in the neutralizing layer of the image-receiving elementas a salt of the polymeric acid in accordance with this invention, wasmade available to the photosensitive element at temperatures above 75 Fespecially at 1 15 F., to give significantly less D loss and balanceshift than shown by the control with o-benzylamino purine disposed onlyin the processing composition. The data also indicate that the TABLE 2Control lma c-rcccivin Elemcnt Temp. 40F 75F 100F 1 F Color R G B R G BR G B R G B D,,,,, 2.50 2.32 2.05 2.55 2.40 2.02 1.90 1.54 1.40 1.301.34 1.24 A from 0.05 0.08 +0.03 0.65 0.86 0.62 l.25 l.06 0.78 75F 0.750.71 0.97 1.06 1.25 1.37 1.45 1.53 1.78 1.78 1.89 1.64, 1.66 Speed Afrom 0.54 0.40 0.39 +0.28 +0.41 +0.33 +0.64 +0.27 +0.21 75F Balance 0.26+0.09 0. 12 +0.08 0.25 0.00 +0.25 +0.02 A from 0.14 +0.01 0.l3 0.08+0.37 0.06 75F Test lmugc-rccciving Element Temp. 40F 75F 100F 1 15FColor R G B R G B R G B R G B 1),, 2.37 2.26 1.97 2.35 2.33 1.94 1.881.64 1.42 1.85 1.87 1.57 A from +0.02 0.07 +0.03 0.47 0.29 -0.52 0.500.46 0.37 75F 0.75 0.70 0.95 1.00 1.21 1.31 1.37 1.46 1.68 1.67 1.541.48 1.49 Speed A from 0.51 0.36 0.37 +0.25 +0.37 +0.30 +0.33 +0.17+0.12 75F Balance 0.25 +0.05 0. 10 +0.06 0.22 0.01 +0.06 +0.01 A from0.15 0.01 0.12 0.07 +0.16 0.05 75F 6-benzylamino purine was releasedfrom the salt faster as the temperature was increased, thus making thisparticular embodiment of the present invention especially useful inminimizing sensitometric changes resulting from elevated processingtemperatures.

Since certain changes may be made in the above product and processwithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description and examplesshall be interpreted as illustrative and not in a limiting sense.

What is claimed is: l. A process for fonning a diffusion transfer dyeimage which comprises:

applying an aqueous alkaline processing composition to an exposedphotosensitive element which includes a silver halide emulsion layerhaving associated therewith a dye image-providing material, therebyinitiating development of exposed silver halide; and forming as afunction of said development an imagewise distribution of mobile dyeimage-providing material which is transferred, at least in part, to asuperposed image-receiving layer to impart thereto a dye image;

said process being performed in the presence of a non-diffusible saltincorporated within the film unit comprising said photosensitive elementand said image-receiving layer, said salt having an anion derived froman immobile polymeric acid and a cation derived from an azole compoundcapable of protonation at a pH below 7 and adapted to control thedevelopment of silver halide, said cation being rendered diffusible tosaid silver halide when said salt is contacted by said processingcomposition.

2. A process as defined in claim 1 wherein said salt is contacted bysaid processing composition after a predetermined period of time haselapsed from the application of said processing composition, therebydelaying the introduction of said development controlling reagent.

3. A process as defined in claim 1 wherein said processing compositioninitially includes said development controlling reagent in its activeform.

4. A process as defined in claim 1 carried out at a temperature above F.

5. A process as defined in claim 1 wherein said azole compound is a4-azabenzimidazole.

6. A process as defined in claim 1 wherein said azole compound is a6-alkylamino purine of the formula:

N//\H/N 'W/ wherein R is an alkyl group.

7. A process as defined in claim 7 wherein said 6- alkylamino purine is6-benzylamino purine.

8. A process as defined in claim 1 wherein said polymeric acid providesa pH in the range of about 2 to about 5.

9. A process as defined in claim 1 wherein said salt is an acid saltwhich is employed as an acid-reacting reagent for lowering theenvironmental pH of said film unit following processing with saidalkaline processing composition.

10. A process as defined in claim 1 wherein said dye image-providingmaterial is a dye developer.

11. A process as defined in claim 1 wherein a redsensitive silver halideemulsion, a green-sensitive silver halide emulsion and a blue-sensitivesilver halide emulsion are present in said photosensitive element, saidsilver halide emulsions having associated therewith, respectively, acyan dye developer, a magenta dye developer and a yellow dye developer,and said dye image is a multicolorimage.

12. A photographic product for forming a diffusion transfer dye imagewhich comprises:

a film unit comprising a photosensitive element including at least onesilver halide emulsion layer having associated therewith a dyeimage-providing material; and an image-receiving element including atleast an image-receiving layer;

means providing an aqueous alkaline processing composition forinitiating development of said silver halide emulsion afterphotoexposure to form thereby an imagewise distribution of mobile dyeimage-providing material which is transferred, at least in part, to saidimage-receiving layer to impart thereto a dye image; and

incorporated within said film unit, a non-diffusible salt having ananion derived from an immobile polymeric acid and a cation derived froman azole compound capable of protonation at a pH below 7 and adapted tocontrol the development of silver halide, said cation being rendereddiffusible to said silver halide when said salt is contacted by saidprocessing composition.

13. A photographic product as defined in claim 12 wherein saidnon-diffusible salt layer is disposed in said image-receiving element.

14. A photographic product as defined in claim 13 wherein saiddevelopment controlling reagent is also disposed in its active form insaid processing composition.

15. A photographic product as defined in claim 12 wherein said dyeimage-providing material is a dye developer.

16. A photographic product as defined in claim 13 wherein said azolecompound is a 4-azabenzimidazole.

17. A photographic product as defined in claim 13 wherein said azolecompound is a 6-alkylamino purine of the formula:

' R-NH Ill I where R is an alkyl group.

18. A photographic product as defined in claim 17 wherein said6-alkylamino purine is 6-benzylamino punne.

19. A photographic product as defined in claim 17 which includes asulfur-free silver solvent in said processing composition.

20. A photographic product as defined in claim 12 wherein said polymericacid provides a pH in the range of about 2 to about 5.

21. A photographic product as defined in claim 12 which furthercomprises a neutralizing layer for lowering the environmental pH uponcontact with said aqueous alkaline processing composition, saidneutralizing layer including a polymeric acid having a plurality of acidgroups.

22. A photographic product as defined in claim 21 wherein saidnon-diffusible salt is disposed in said neutralizing layer.

23. A photographic product as defined in claim 22 wherein saidneutralizing layer is disposed in said image-receiving element.

24. A photographic product as defined in claim 22 wherein the anion ofsaid salt is derived from the polymeric acid of said neutralizing layerto provide the acid-reacting reagent of said neutralizing layer.

25. A photographic product as defined in claim 24 wherein said polymericacid is the half butyl ester of poly (ethylene/maleic anhydride).

26. A photographic product as defined in claim 12 wherein saidphotosensitive element and said imagereceiving element are retainedtogether as an integral positive-negative film unit including meansproviding a light-reflecting layer between said image-receiving layerand said silver halide emulsion (s) sufficient to mask effectively saidsilver halide emulsion (s) after development thereof and provide abackground for viewing said dye image, and a transparent support throughwhich said dye image may be viewed.

27. A photographic product as defined in claim 26 wherein said meansproviding a light-reflecting layer comprises a white pigment dispersedin said processing composition, and said processing composition iscontained in a rupturable container positioned to distribute saidprocessing composition containing said pigment between saidimage-receiving layer and said silver halide emulsion (s).

28. An image-receiving element for use in diffusion transfer processes,comprising an image-receiving layer having associated therewith anon-diffusible salt with an anion derived from an immobile polymericacid and a cation derived from a reagent adapted to control thedevelopment of silver halide.

29. An image-receiving element as defined in claim 28 wherein saidnon-diffusible salt is disposed in a separate layer adjacent to saidimage-receiving layer.

30. An image-receiving element as defined in claim 29 wherein saidseparate layer is a neutralizing layer for lowering the environmental pHupon contact with an aqueous alkaline processing composition, saidneutralizing layer including a polymeric acid having a plurality of acidgroups.

31. An image-receiving element as defined in claim 30 wherein the anionof said salt is derived from the polymeric acid of said neutralizinglayer to provide the acid-reacting reagent in said neutralizing layer.

32. An image-receiving element as defined in claim 30 further comprisinga polymeric timing layer disposed between said image-receiving layer andsaid neutralizing layer.

33. An image-receiving element as defined in claim 28 wherein saidpolymeric acid provides a pH in the range of about 2 to about 5.

34. An image-receiving element as defined in claim 33 wherein saidpolymeric acid is the half butyl ester of poly (ethylene/maleicanhydride).

35. An image-receiving element as defined in claim 33 wherein saiddevelopment controlling reagent is an azole compound capable ofprotonation in said pH range.

36. An image-receiving element as defined in claim 35 wherein said azolecompound is a 4- azabenzimidazole.

37. An image-receiving element as defined in claim 35 wherein said azolecompound is a 6'-alkylamino purine of the formula:

wherein R is an alkyl group.

38. An image-receiving element as defined in claim 37 wherein said6-alkylamino purine is 6-benzylamino purine.

39. An integral positive-negative film unit comprising in sequence,

a first dimensionally stable support;

a red-sensitive silver halide emulsion having associated therewith acyan dye-developer;

a green-sensitive silver halide emulsion having associated therewith amagenta dye-developer;

a blue-sensitive silver halide emulsion having associated therewith ayellow dye-developer;

a dyeable polymeric layer;

a neutralizing layer comprising a non-diffusible salt having an anionderived from an immobile polymeric acid and a cation derived from anazole compound adapted to control the development of silver halide, saidcation being rendered diffusible to at least one of said silver halideemulsions upon contact with an aqueous alkaline processing composition,said salt effecting a reduction of the pH of said processing compositionfrom a first pH at which said dye developers and said cation are solubleand diffusible to at least a second lower pH at which said dyedevelopers are substantially insoluble and non-diffusible;

a second dimensionally stable support which is transparent;

means securing at least the side edges of said layers in fixedrelationship; and

a rupturable container retaining said aqueous alkaline processingcomposition having said first pH and containing dispersed therein awhite inorganic pigment in a quantity sufficient to mask effectivelysaid silver halide layers and any dye developer associated therewithafter development and to provide a background for viewing by reflectedlight, through said transparent layer, a diffusion transfer image issaid dyeable layer formed by development of said film unit, saidrupturable container being fixedly positioned to distribute saidprocessing composition containing said pigment between said dyeablelayer and said silver halide emulsions.

40. A film unit as defined in claim 39 wherein said dye developers aredisposed in separate layers adjacent their respective silver halideemulsion layers.

41. A film unit as defined in claim 40 further comprising an aqueouspolymeric timing layer disposed between said dyeable layer and saidneutralizing layer.

42. A film unit as defined in claim 43 wherein said azole compound is a6-alkylamino purine of the formula:

maleic anhydride).

2. A process as defined in claim 1 wherein said salt is contacted by said processing composition after a predetermined period of time has elapsed from the application of said processing composition, thereby delaying the introduction of said development controlling reagent.
 3. A process as defined in claim 1 wherein said processing composition initially includes said development controlling reagent in its active form.
 4. A process as defined in claim 1 carried out at a temperature above 75* F.
 5. A process as defined in claim 1 wherein said azole compound is a 4-azabenzimidazole.
 6. A process as defined in claim 1 wherein said azole compound is a 6-alkylamino purine of the formula:
 7. A process as defined in claim 7 wherein said 6-alkylamino purine is 6-benzylamino purine.
 8. A process as defined in claim 1 wherein said polymeric acid provides a pH in the range of about 2 to about
 5. 9. A process as defined in claim 1 wherein said salt is an acid salt which is employed as an acid-reacting reagent for lowering the environmental pH of said film unit following processing with said alkaline processing composition.
 10. A process as defined in claim 1 wherein said dye image-providing material is a dye developer.
 11. A process as defined in claim 1 wherein a red-sensitive silver halide emulsion, a green-sensitive silver halide emulsion and a blue-sensitive silver halide emulsion are present in said photosensitive element, said silver halide emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer, and said dye image is a multicolor image.
 12. A photographic product for forming a diffusion transfer dye image which comprises: a film unit comprising a photosensitive element including at least one silver halide emulsion layer having associated therewith a dye image-providing material; and an image-receiving element including at least an image-receiving layer; means providing an aqueous alkaline processing composition for initiating development of said silver halide emulsion after photoexposure to form thereby an imagewise distribution of mobile dye image-providing material which is transferred, at least in part, to said image-receiving layer to impart thereto a dye image; and incorporated within said film unit, a non-diffusible salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound capable of protonation at a pH below 7 and adapted to control the development of silver halide, said cation being rendered diffusible to said silver halide when said salt is contacted by said processing composition.
 13. A photographic product as defined in claim 12 wherein said non-diffusible salt layer is disposed in said image-receiving element.
 14. A photographic product as defined in claim 13 wherein said development controlling reagent is also disposed in its active form in said processing composition.
 15. A photographic product as defined in claim 12 wherein said dye image-providing material is a dye developer.
 16. A photographic product as defined in claim 13 wherein said azole compound is a 4-azabenzimidazole.
 17. A photographic product as defined in claim 13 wherein said azole compound is a 6-alkylamino purine of the formula:
 18. A photographic product as defined in claim 17 wherein said 6-alkylamino purine is 6-benzylamino purine.
 19. A photographic product as defined in claim 17 which includes a sulfur-free silver solvent in said processing composition.
 20. A photographic product as defined in claim 12 wherein said polymeric acid provides a pH in the range of about 2 to about
 5. 21. A photographic product as defined in claim 12 which further comprises a neutralizing layer for lowering the environmental pH upon contact with said aqueous alkaline processing composition, said neutralizing layer including a polymeric acid having a plurality of acid groups.
 22. A photographic product as defined in claim 21 wherein said non-diffusible salt is disposed in said neutralizing layer.
 23. A photographic product as defined in claim 22 wherein said neutralizing layer is disposed in said image-receiving element.
 24. A photographic product as defined in claim 22 wherein the anion of said salt is derived from the polymeric acid of said neutralizing layer to provide the acid-reacting reagent of said neutralizing layer.
 25. A photographic product as defined in claim 24 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).
 26. A photographic product as defined in claim 12 wherein said photosensitive element and said image-receiving element are retained together as an integral positive-negative film unit including means providing a light-reflecting layer between said image-receiving layer and said silver halide emulsion (s) sufficient to mask effectively said silver halide emulsion (s) after development thereof and provide a background for viewing said dye image, and a transparent support through which said dye image may be viewed.
 27. A photographic product as defined in claim 26 wherein said means providing a light-reflecting layer comprises a white pigment dispersed in said processing composition, and said processing composition is contained in a rupturable container positioned to distribute said processing composition containing said pigment between said image-receiving layer and said silver halide emulsion (s).
 28. An image-receiving element for use in diffusion transfer processes, comprising an image-receiving layer having associated therewith a non-diffusible salt with an anion derived from an immobile polymeric acid and a cation derived from a reagent adapted to control the development of silver halide.
 29. An image-receiving element as defined in claim 28 wherein said non-diffusible salt is disposed in a separate layer adjacent to said image-receiving layer.
 30. An image-receiving element as defined in claim 29 wherein said separate layer is a neutralizing layer for lowering the environmental pH upon contact with an aqueous alkaline processing composition, said neutralizing layer including a polymeric acid having a plurality of acid groups.
 31. An image-receiving element as defined in claim 30 wherein the anion of said salt is derived from the polymeric acid of said neutralizing layer to provide the acid-reacting reagent in said neutralizing layer.
 32. An image-receiving element as defined in claim 30 further comprising a polymeric timing layer disposed between said image-receiving layer and said neutralizing layer.
 33. An image-receiving element as defined in claim 28 wherein said polymeric acid provides a pH in the range of about 2 to about
 5. 34. An image-receiving element as defined in claim 33 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride).
 35. An image-receiving element as defined in claim 33 wherein said development controlling reagent is an azole compound capable of protonation in said pH range.
 36. An image-receiving element as defined in claim 35 wherein said azole compound is a 4-azabenzimidazole.
 37. An image-receiving element as defined in claim 35 wherein said azole compound is a 6-alkylamino purine of the formula:
 38. An image-receiving element as defined in claim 37 wherein said 6-alkylamino purine is 6-benzylamino purine.
 39. An integral positive-negative film unit comprising in sequence, a first dimensionally stable support; a red-sensitive silver halide emulsion having associated therewith a cyan dye-developer; a green-sensitive silver halide emulsion having associated therewith a magenta dye-developer; a blue-sensitive silver halide emulsion having associated therewith a yellow dye-developer; a dyeable polymeric layer; a neutralizing layer comprising a non-diffusible salt having an anion derived from an immobile polymeric acid and a cation derived from an azole compound adapted to control the development of silver halide, said cation being rendered diffusible to at least one of said silver halide emulsions upon contact with an aqueous alkaline processing composition, said salt effecting a reduction of the pH of said processing composition from a first pH at which said dye developers and said cation are soluble and diffusible to at least a second lower pH at which said dye developers are substantially insoluble and non-diffusible; a second dimensionally stable support which is transparent; means securing at least the side edges of said layers in fixed relationship; and a rupturable container retaining said aqueous alkaline processing composition having said first pH and containing dispersed therein a white inorganic pigment in a quantity sufficient to mask effectively said silver halide layers and any dye developer associated therewith after development and to provide a background for viewing by reflected light, through said transparent layer, a diffusion transfer image is said dyeable layer formed by development of said film unit, said rupturable container being fixedly positioned to distribute said processing composition containing said pigment between said dyeable layer and said silver halide emulsions.
 40. A film unit as defined in claim 39 wherein said dye developers are disposed in separate layers adjacent their respective silver halide emulsion layers.
 41. A film unit as defined in claim 40 further comprising an aqueous polymeric timing layer disposed between said dyeable layer and said neutralizing layer.
 42. A film unit as defined in claim 43 wherein said azole compound is a 6-alkylamino purine of the formula:
 43. A film unit as defined in claim 42 wherein said 6-alkylamino purine is 6-benzylamino purine.
 44. A film unit as defined in claim 43 which includes an additional amount of said 6-benzylamino purine in said processing composition.
 45. A film unit as defined in claim 43 wherein said polymeric acid provides a pH of about
 2. 46. A film unit as defined in claim 45 wherein said polymeric acid is the half butyl ester of poly (ethylene/maleic anhydride). 